The prior art is how using FIG. 1, which is an exemplary embodiment for a fuel quantity setting arrangement, as is known from DE-C2-24 57 436.
In the known arrangement, the setting system consists of a single setting unit, which is designed as a combined open-loop/closed-loop control unit. This open-loop/closed-loop control unit is supplied signals from a sensor arrangement 11, that is the signal of a speed sensor and the signal of a throttle-flap sensor. From these signals, the air volume taken in by the engine corresponding thereto can be determined. From this air volume, the open-loop/closed-loop control unit computes a corresponding quantity of fuel and determines the value of a manipulated variable, which is supplied to a fuel injection pump 12. The manipulated variable is predetermined from a throttle-flap/speed characteristic map and modified by a multiplicative factor, which depends on the difference between a lambda desired value fixed for the closed-loop control unit and a lambda actual value, as is emitted by a lambda probe 13, acting as output sensor, to the controlling setting unit 10.
This is consequently an open-loop control with subsequent closed-loop control, by which the value of the manipulated variable follows the value of the signals emitted by the speed sensor and by the throttle-flap sensor. The open-loop control has a very fast response performance, since a change in the signals of the speed sensor and/or of the throttle-flap sensor is converted directly into a changed manipulated variable. However, whether this fast conversion was correct only becomes apparent when the lambda probe 13 reports back the new lambda actual value. This happens with a transient response period of about half a second to several seconds. If, due to the measurement of the lambda probe arrangement, a deviation between lambda desired value and lambda actual value is established, the multiplicative factor for calculating the manipulated variable is determined anew by the controlling part of the setting unit 10.
In the known arrangement, there exists for example the problem that, with the aid of the speed sensor and the throttle-flap sensor, the air volume is determined, but not the air mass, which is actually what is important for the metering of the quantity of fuel. Therefore, in the prior art, air-mass sensors in the form of hot-wire air-mass sensors or hot-film air-mass sensors are used as sensor arrangements. These allow quite an accurate determination of the air mass.
The advantage of air-mass sensors with respect to the measuring accuracy of the variable which is actually to be monitored is, however, also offset by disadvantages. Although hot-film air-mass sensors can be produced cheaply and robustly, they then operate relatively slowly.
U.S. Pat. No. 4,712,529 is cited as further state of the art. This publication relates to an "air/fuel-ratio control arrangement for transition conditions during operation of an internal combustion engine". The metered fuel quantity is here determined in dependence upon the air throughput in the intake pipe. However, because air mass measuring arrangements exhibit an inertia caused by physical conditions, measures are taken for making ready a quickest possible effective acceleration enrichment. For this purpose, especially the output signal of a throttle-flap position sensor serves which acts in a corrective manner on the basic fuel metering signal dependent upon the air throughput. With this state of the art, the premise is taken that the fuel metering signal is formed from the air mass throughput signal and a signal from the throttle flap position sensor acts correctively.
In addition, a fuel metering system is known from US-A-4 594 987 wherein, corresponding to FIG. 9, likewise the throttle flap position signal is applied to form a corrective variable.
Finally, JP-A-61 58 945 disclosed a safety system in combination with the fuel metering in an internal combustion engine such that the output signals of two sensors, which respond to the air throughput in the intake pipe, are compared with each other and a malfunction determination is made possible in correspondence to the results.